Hi I'm Ness, I'm from Alabama & I have a 2004 4.8 Chevy Silverado with 138k miles. I was wondering if anyone else uses marvel mystery oil in their trucks? I asked my farther to use Lucas because that's what I prefer. My main question is, if you do use marvel does it set off the check engine light for your knock sensors? 3 times he's used it, 3 times it's gone off, once it cycles out of the engine the light goes off.

Marvel oil is basically transmission fluid on steroids, as with transmission fluid, it has tremendous cleansing ability. I used it 15 to 20 years ago in the oil, and in the gasoline, however with the oil refinement now a days (sn vs. sa) with the sulfer removed, and the refinement of gasoline, the marvel oil is basically an outdated dinasor.

My dad puts it in there, I don't use it ever, if I do put anything it's Lucas products. I know once it's run itself out of the system the check engine light will go off. Just curious if anyone else had this happen.

I've used it in the gasoline and in the oil just before a change. Never a problem. Lot's of people look at it as snake oil, but in my experience in the gas, it makes the truck idle much smoother. Just don't overdo the amount.

Also I had a piece of lawn equipment (bought used) that burned oil. I pulled the plug and poured MMO on top of the piston for a soak. Left it alone for about a week. It dissolved the crud around the rings and no more oil burning.

I don't go crazy with the amount, but a little before an oil change in my opinion helps keep everything clean.

Its been around since 1923, so if it didn't do something, I doubt they would have stayed in business this long.

My 1992 Mercury Grand Marquis is still running great at 170,000 miles. Never any injector, fuel pump, or fuel tank problems.
I also have this vehicle oil undercoated every year. I reside in heavy winter salt area. No rust so far. No replacement of gas tank, fuel lines etc.

"I lived to tell the story, but did not tell the story to live". Diego Garcia

I'm having the same code going off also on an 05 5.3. Changed the water pump and pressure washed the motor afterwards to clean up the mess. P0420 knock sensor code started going off after that. Seems the 5.3 & the 6.0 are prone to getting carbon build up on the pistons so I did the water injection trick to clean it up. 1/4" clear tube stuck on the PVC valve inlet on top of intake plenum. rev engine to around 2500 rpm and drop the 8' long piece of tubing in a gallon of water (small amounts!!!). Thsi will steam clean the inside of the engine if done correctly and it really seemed to help, it idles so smoothly that you can't even tell it's running.

Anyways, just did this yesterday and will wait and see if the knock sensor code goes away or if I need to replace them because I got them wet washing the engine bay.

Knock sensors are also one of the most common problems you can have on the Gen 3's as well. The harness and the sensor itself corrode away because they trap moisture where they are mounted in the valley cover. Pull the intake, change the sensors and the harness plus make a little dam around the sensor hole in the valley cover with RTV and you are good to go.

Most guys say never to pressure wash a Gen 3 specifically because of this..... but whatever. I do everytime I wash my one truck and with over 100000 miles and 8 model years old it's yet to trip a CEL for a knock sensor. They fail regardless and heat and air humidity are your biggest killer.